23Na, 29Si, and 13C MAS NMR investigation of glass-forming reactions between Na2CO3 and SiO2
23Na, 29Si, and 13C MAS NMR investigation of glass-forming reactions between Na2CO3 and SiO2
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DOI：
10.1021/jp053953y
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发表时间：
2005-12-15
影响因子：
3.3
通讯作者：
Smith, IH
中科院分区：
文献类型：
--
作者：
Jones, AR;Winter, R;Smith, IH
碳酸钠 (Na2CO3) 和二氧化硅 (SiO2) 之间的玻璃形成反应已通过 Na-23、Si-29 和 C-13 魔角旋转 (MAS) NMR 光谱进行了研究。多核 MAS NMR 方法可识别和量化反应产物和中间体（玻璃状和结晶状）。在不同温度下进行等温和非等温热处理后，对一系列初始成分 Na(2)CO(3) 中心点 chi SiO2 (chi = 1, 2) 的粉末批次进行了研究，这些粉末批次对应于偏硅酸钠 (Na2SiO3) 和二硅酸钠 (Na2Si2O5) 化学计量。对 Na-23 四极耦合参数的分析已确定所有情况下的早期反应产物均为结晶 Na2SiO3。在非等温实验中，该反应之前是在 850 摄氏度左右形成的早期富硅熔融相。早期反应受晶粒界面层反应区中固态 Nal 扩散的控制。结晶Na2SiO3在界面层中析出，增加了Na2CO3和SiO2晶粒之间的厚度，并减慢了Na2迁移速率。这会产生第二相，该相与温度有关。在低温下，Na+ 迁移受到损害，Na2SiO3 的生成停止，富含二氧化硅的相沉淀出来。在二硅酸钠批料的情况下，存在过量的SiO2，观察到Na2SiO3与SiO2的二次反应，形成玻璃相。通过 C-13 NMR 鉴定出瞬态含碳相为 NaCO3 复合物，与 SiO2 颗粒表面硅酸盐网络中的桥氧松散结合。
The glass-forming reactions between sodium carbonate (Na2CO3) and silica (SiO2) have been investigated by Na-23, Si-29, and C-13 magic-angle spinning (MAS) NMR spectroscopy. The multinuclear MAS NMR approach identifies and quantifies reaction products and intermediates, both glassy and crystalline. A series of powdered batches of initial composition Na(2)CO(3)center dot chi SiO2 (chi = 1, 2) corresponding to a sodium metasilicate (Na2SiO3) and sodium disilicate (Na2Si2O5) stoichiometry were investigated after periods of isothermal and nonisothermal heat treatments at different temperatures. Analysis of the Na-23 quadrupolar coupling parameters has identified the early reaction product in all cases as crystalline Na2SiO3. In the nonisothermal experiment, this reaction is preceded by an early silica-rich melt phase formed around 850 degrees C. The early reactions are controlled by solid-state Nal diffusion across the reaction zone in the grain interface layer. Crystalline Na2SiO3 precipitates in the interface layer, increasing its thickness between the Na2CO3 and the SiO2 grains and slowing down the rate of Nal migration. This creates a secondary phase, which is temperature dependent. At low temperatures, where Na+ migration is impaired, the production of Na2SiO3 ceases and silica-richer phases are precipitated. In the case of the sodium disilicate batch, where excess SiO2 is present, a secondary reaction of Na2SiO3 with SiO2 forming a glassy phase is observed. A transient carbon-bearing phase has been identified by C-13 NMR as a NaCO3- complex loosely bound to bridging oxygens in the silicate network at the SiO2 grain surface.